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Reproduction of a Damage Belt in Downtown Mashiki, Kumamoto, Japan Considering Liquefaction Effects on Estimated Ground Motions

Session: How Well Can We Assess Site Effects So Far? II

Type: Oral

Date: 4/20/2021

Presentation Time: 03:30 PM Pacific

Description: 

A building damage belt was generated in Mashiki Town along the local Road 28 of Kumamoto prefecture, Japan, during the mainshock of 2016 Kumamoto earthquake in Japan. The building damage distribution based on the ground motions estimated by the equivalent linear analysis (ELA) was obtained. However, the estimated building damage probabilities in the area near the Akitsu river, where soil liquefaction was observed by the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT), were larger than the field survey results published by the Architectural Institute of Japan (AIJ). Thus, we need to discuss the effects of soil liquefaction on the strong ground motions and subsequently the local building damages during the mainshock. Nonlinear analysis (NA) which combines the Ramberg–Osgood (RO) relationship and Bowl model were performed to study soil liquefaction. Moreover, the nonlinear structural analysis model was used to estimate the building damage probability of wooden houses (WDP). 592 one–dimensional velocity structures, the seismological bedrock (Vs = 3.4 km/s) ground motions, construction periods of wooden houses, and distribution of water table depth were obtained for Mashiki. Nonlinear properties of four borehole drilling sites in Mashiki were constructed based on the laboratory tests, and 592 sites were classified into four categories. Finally, the estimated soil liquefaction distribution was similar to the MLIT field survey results. The PGV distributions by NA showed similar to that by ELA, and they were correlated to the AIJ building damage distribution. Both the estimated PGAs and PGVs by NA were smaller than that of ELA, which indicates the strong effects of nonlinear soil properties, especially in the soil liquefaction area. Furthermore, the NA–WDP distribution was similar to the field survey by AIJ, and also similar to ELA–WDP distribution, except for the liquefaction area where NA–WDPs were obviously smaller than ELA–WDPs. Thus, the soil liquefaction has a strong effect to decrease the estimated ground motions and subsequent structure damages.

Presenting Author: Jikai Sun

Student Presenter: Yes

Authors